extracting DEM data

Wang Song wang at cast.uark.edu
Tue Nov 23 16:37:23 EST 1993

 gurcharan s khanna writes:

> 1) is there a tutorial for m.dem.extract or other ways to import DEM files?

> 2) otherwise, here is what i am trying:
>	a) obtained DEM files from usgs ftp site.
>	b) start grass set to my LA database
>	c) use g.region to set region to something slightly larger than
>	   the header info from the DEM indicates
>		set res to 00:00:03
>	b) using m.dem.extract to extract data
>	   setting start and end file number = 1
>	c) data extraction completes successfully with 1201 rowsxcols
>	d) d.erase; d.rast shows only single color for entire display

> am i missing some step? i even tried changing the color table with r.colors,
> and running r.support explicitly, but with no change.  i can display my
> Tiger data maps without any problems. any help would be appreciated.

	Check the block size you used in extraction. You may try some different
blocksizes such as 4096, 10240, 1024, etc. In addition, 1201 rowsxcols looks 
too small for 7.5 minute DEM which has 30-meter resolution.

	Don't be confused with the progress made on m.dem.extract. It could 
still have problems though the program runs through without complaint.

Song Wang
CAST, 12 Ozark Hall
University of Arkansas
Fayetteville, AR 72701

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